This application claims priority to an application entitled xe2x80x9cRLP Communication Device and Method for Mobile Communication Systemxe2x80x9d filed in the Korean Industrial Property Office on Oct. 15, 1998 and assigned Ser. No. 98-43560, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to a CDMA (Code Division Multiple Access) mobile communication system, and in particular, to an RLP (Radio Link Protocol) communication device and method which supports a discontinuous transmission (DTX) mode for an effective data transmission in a radio environment.
2. Description of the Related Art
CDMA mobile communication systems have developed from the voice service-based IS-95 standard into the CDMA-2000 standard which provides not only voice service but also a high-speed data transmission service as well. For example, the CDMA-2000 standard provides high-quality voice service, moving picture service, Internet search service, etc. The existing voice service-based CDMA mobile communication system transmits data at a data rate of 9.6 Kbps or 14.4 Kbps, whereas the CDMA-2000 mobile communication system transmits data at a rate of up to 2 Mbps. Therefore, the CDMA-2000 system can transmit data over 138 times faster than the existing CDMA mobile communication system.
The CDMA mobile communication system uses a radio link protocol (RLP) to solve a data loss problem which occurs in a radio environment. The radio link protocol is based on a 20 ms frame at a data rate of below 9.6 or 14.4 Kbps, and an RLP Type 2 has been proposed.
The radio link protocol uses a NAK (Non-Acknowledge) method to limit data loss. A receiving side requests a transmission side to retransmit only the receiving-failed RLP frames. In this method, however, the receiving side does not know of the receiving failure for a specific frame until a frame having a sequence number higher than that of the receiving-failed frame is received.
Referring to FIG. 1, there is shown a case where only the fifth frame out of five frames transmitted from the transmission side has successfully arrived at the receiving side. Therefore, in FIG. 1, the receiving side cannot recognize the receiving failure for the first to fourth frames until the fifth frame is received.
As mentioned above, the radio link protocol uses the NAK method, so that the receiving side does not immediately recognize the receiving failure of a frame. Therefore, in the existing RLP Type 2, idle frames are used to solve the above problem. In. RLP Type 2, the transmission side transmits an idle frame when there is no frame to transmit so as to inform the receiving side about the sequence number of the last transmitted data frame. That is, the transmission side constantly transmits frames, and if any one of the transmitted frames is received, the receiving side immediately knows which frame or frames it failed to receive. By using this method, the receiving side can determine a failed-receipt in a much shorter period of time. Unfortunately, the constant transmission of idle frames overloads the system. Furthermore, unlike the IS-95 standard, the CDMA-2000 standard is not required to transmit frames continuously. It is therefore ineffective to use the method of transmitting the idle frames to solve the problem of the NAK method.
The RLP Type 2 proposes a method of using an idle timer and an idle transmission counter. In this method, the idle timer is set to a specific value when there is no data to be transmitted, and thereafter, when the idle timer becomes 0 (zero), the idle transmission counter is increased by one after transmitting one idle frame. Then, the idle timer is set again to the specific value, and thereafter, when the idle timer becomes 0, the idle transmission counter is increased by one after transmitting one idle frame. This operation is repeated until the idle transmission counter becomes 3, and then, transmission of the idle frames is discontinued. In this method, transmission of the idle frames is immediately discontinued when there is data to transmit; and after transmission was discontinued because the idle transmission counter became 3, transmission is not restarted until there is data to transmit.
The above method is advantageous because there is a reduction in the system load due to the idle timer. That is, in the RLP Type 2, when an RLP frame is receiving-failed, a blank frame is unconditionally made in a physical layer and a multiplexing layer of the receiving side. However, in this case, the radio link protocol does not know whether the radio link protocol of the transmission side failed to transmit the RLP frame because there is no data to transmit or there is data to transmit but there is no opportunity to transmit data because another service has a higher priority. In this case, it is determined in the RLP Type 2 that data was not transmitted because of the service having a higher priority and that there is data waiting to transmit. In other words, in the RLP Type 2, retransmission-related timers are not decreased, thus delaying transmission.
The CDMA-2000 standard provides a method for enabling the receiving side to recognize that the transmission side did not transmit data, whereby a transmission side of the physical layer transmits no physical channel frame. By using this above method, the radio link protocol can distinguish whether the radio link protocol of the transmission side either has no data to transmit or has low priority. It is therefore possible to facilitate a more accurate operation by using the function of the physical layer.
It is, therefore, an object of the present invention to provide a method in which a radio link protocol (RLP) can operate in an environment where periodic frame transmission is not guaranteed.
It is another object of the present invention to provide a method in which a physical layer of a receiving side informs a radio link protocol that no physical frame has been received.
It is further another object of the present invention to provide a method in which a transmission side can efficiently verify whether or not the last data in a continuous transmission duration is transmitted normally in a discontinuous transmission environment.
It is yet another object of the present invention to provide a method for decreasing a retransmission timer when data is not transmitted in a discontinuous transmission mode so as to ensure efficient retransmission.
It is still another object of the present invention to provide an improved RLP communication device and method for suppressing the transmission of idle frames when there in no data to transmit in a mobile communication system, thus reducing the system load.
It is still another object of the present invention to provide an improved RLP communication device and method for controlling the transmission of the idle frames according to a condition of the physical channel.
It is still another object of the present invention to provide an improved RLP communication device and method for transmitting a frame having control information other than idle frames, so as to obtain the same result as if idle frames were transmitted, thereby improving the performance.
It is a further object of the present invention to provide an improved RLP communication device and method for transmitting a frame with control information using an automatic repeat request (ARQ) function, to verify whether or not every frame has been correctly transmitted.
To achieve the above objects, there is provided an RLP communication method for a mobile communication system. In the RLP communication method, an RLP layer transfers an information frame including information about a transmission side to a physical layer/multiplexing layer at set periods when there is no data to transmit. The physical layer/multiplexing layer receives the information frame and transmits the received information frame to the other party over a physical channel.